Freight elevators which are used in warehouses, commercial buildings, and various industrial applications, differ from general purpose or passenger elevators in several respects. Although the actual carriage or car of both types of elevators are essentially the same, neglecting the size and decor thereof, the doors, and mechanisms for the operation of the doors to the elevator differ. Furthermore, freight elevators are generally subject to different codes and regulations.
Generally, passenger elevators have two sets of horizontally-opening doors. One set of doors moves with the elevator carriage while the other set of doors is fixed to the hoistway opening on the respective floor. Both sets of doors include left and right halves that join together along a vertical line and thus horizontally outwardly open. When the passenger elevator carriage reaches the respective floor, both sets of doors then open to allow passengers to enter and egress.
In contrast, freight elevators generally have vertically opening doors. The vertically opening doors may be either a single set of doors affixed to the hoistway opening of the respective floor or a single vertically opening door. The single set of vertical doors includes two half doors meeting at a horizontal line and respectively opening in a vertical bi-directional manner while the single door moves vertically. The elevator carriage generally includes a single vertically-moving gate or door which travels along with the elevator carriage. Both the passenger elevators and freight elevators include systems therein which control the opening and closing of the respective doors. Various regulations and safety codes require that such doors positively open and close.
In the case of freight elevators, safety codes require that the doors to the hoistway physically lock when the elevator is not present at the particular floor. Therefore, all of the doors to the hoistway need to be locked when the elevator is in motion. When the elevator stops at any individual floor, then, and only then, should the particular set of doors to the that particular floor be able to open. This is generally accomplished by providing a positive locking mechanism at each floor that is also electrically interlocked so that in the case of some possible action that would unlock a door at a particular floor which should not be unlocked, the elevator carriage will stop and no other action may take place. Such prior art locking mechanisms are thus located at each floor.
It is necessary for the contacts in the safety circuit to positively open when needed and freight elevators are generally located in areas which are not always clean, or are subject to becoming dirty quickly, with loading and unloading of various equipment and the like. In this regard, European safety codes specify that such contacts must open even if they are welded shut.
Most prior art interlock systems utilize spring action to positively make contact or "interlock" and another force or positive mechanism is used to break contact. However, such positive mechanisms are not capable of providing the necessary shearing action that may be required to separate the contacts should the contacts become joined together either through welding or the like. Thus, it is desirable to have an interlock system which is capable of positively making and breaking contact in all situations.
Furthermore, prior art interlock systems or ladder switches are composed of many individual components. If it is necessary to repair or change the components due to breakage or corrosion the entire assemblage must be taken apart. Due to the general location of the interlock system within the elevator hoistway, it is generally very difficult to reach and/or effect the modifications.
It is thus desirable to provide an interlock switch which is easy to effect repair.